U.S. patent application number 13/632959 was filed with the patent office on 2014-04-03 for electromechanical systems device with protrusions to provide additional stable states.
This patent application is currently assigned to QUALCOMM MEMS TECHNOLOGIES, INC.. The applicant listed for this patent is QUALCOMM MEMS TECHNOLOGIES, INC.. Invention is credited to Edward Keat Leem Chan, Chong Uk Lee, Isak Clark Reines, Bing Wen.
Application Number | 20140092110 13/632959 |
Document ID | / |
Family ID | 49263433 |
Filed Date | 2014-04-03 |
United States Patent
Application |
20140092110 |
Kind Code |
A1 |
Chan; Edward Keat Leem ; et
al. |
April 3, 2014 |
ELECTROMECHANICAL SYSTEMS DEVICE WITH PROTRUSIONS TO PROVIDE
ADDITIONAL STABLE STATES
Abstract
This disclosure provides systems, methods, and apparatus for an
electromechanical systems (EMS) device with one or more protrusions
connected to a surface of the EMS device. In one aspect, the EMS
device includes a substrate, a stationary electrode over the
substrate, and a movable electrode over the stationary electrode.
The movable electrode is configured to move to three or more
positions across a gap by electrostatic actuation between the
movable electrode and the stationary electrode. When the
protrusions contact any surface of the EMS device at one of the
positions across the gap, the protrusions change the stiffness of
the EMS device. At least one of the surfaces in contact with the
one or more protrusions is non-rigid. In some implementations, the
protrusions have a height greater than about 20 nm.
Inventors: |
Chan; Edward Keat Leem; (San
Diego, CA) ; Reines; Isak Clark; (San Diego, CA)
; Wen; Bing; (Poway, CA) ; Lee; Chong Uk;
(San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM MEMS TECHNOLOGIES, INC. |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM MEMS TECHNOLOGIES,
INC.
San Diego
CA
|
Family ID: |
49263433 |
Appl. No.: |
13/632959 |
Filed: |
October 1, 2012 |
Current U.S.
Class: |
345/530 ; 29/846;
359/290 |
Current CPC
Class: |
B81B 2203/0163 20130101;
H01F 2007/1822 20130101; B81B 3/0051 20130101; B81B 2203/0109
20130101; Y10T 29/49155 20150115; B81B 3/007 20130101; B81B
2201/047 20130101 |
Class at
Publication: |
345/530 ;
359/290; 29/846 |
International
Class: |
G02B 26/00 20060101
G02B026/00; G06T 1/60 20060101 G06T001/60; H05K 3/10 20060101
H05K003/10 |
Claims
1. An electromechanical systems (EMS) device, comprising: a
substrate; a stationary electrode over the substrate; a movable
electrode over the stationary electrode and configured to move to
three or more positions across a gap by electrostatic actuation
between the movable electrode and the stationary electrode; and a
protrusion connected to a surface of the EMS device, wherein the
protrusion is configured to change the stiffness of the EMS device
when in contact with another surface of the EMS device at one of
the positions across the gap, and wherein at least one of the
surfaces in contact with the protrusion is non-rigid.
2. The EMS device of claim 1, further comprising a plurality of
tethers symmetrically disposed around the edges of the movable
electrode, wherein the protrusion is part of a plurality of
protrusions and each of the protrusions is connected to each of the
tethers.
3. The EMS device of claim 2, further comprising a plurality of
posts over the substrate, wherein the movable electrode is
connected to the plurality of posts by the plurality of
tethers.
4. The EMS device of claim 2, wherein the movable electrode
includes a reflective layer having a rigid surface and the
plurality of tethers includes a plurality of hinges each having a
non-rigid surface.
5. The EMS device of claim 1, wherein the protrusion is connected
to a surface of the movable electrode facing the stationary
electrode.
6. The EMS device of claim 1, wherein the protrusion is connected
to a surface of the substrate facing the movable electrode.
7. The EMS device of claim 1, wherein the protrusion is part of a
plurality of protrusions symmetrically disposed about the center of
the movable electrode.
8. The EMS device of claim 1, wherein the EMS device is part of an
optical device.
9. The EMS device of claim 8, wherein the EMS device is part of an
analog interferometric modulator (AIMOD).
10. The EMS device of claim 9, wherein the three or more positions
across the gap correspond to different visible wavelengths in each
of the positions, wherein one of the positions across the gap is
defined at least in part by the height of the protrusion.
11. The EMS device of claim 9, wherein the protrusion defines a
plurality of positions across the gap corresponding to a stable
color range when the protrusion is in contact with another surface
of the EMS device.
12. The EMS device of claim 1, wherein the protrusion has a height
greater than about 20 nm.
13. The EMS device of claim 12, wherein the protrusion has a height
between about 100 nm and about 200 nm.
14. The EMS device of claim 1, wherein the protrusion is part of a
plurality of protrusions, each of the protrusions having a
different height.
15. The EMS device of claim 1, further comprising a top electrode
over the movable electrode, wherein the movable electrode is
configured to move across an upper gap by electrostatic actuation
between the movable electrode and the top electrode.
16. The EMS device of claim 1, wherein the EMS device forms a
display, the display including: a processor that is configured to
communicate with the display, the processor being configured to
process image data; and a memory device that is configured to
communicate with the processor.
17. The EMS device of claim 16, further comprising: a driver
circuit configured to send at least one signal to the display; and
a controller configured to send at least a portion of the image
data to the driver circuit.
18. The EMS device of claim 16, further comprising: an image source
module configured to send the image data to the processor, wherein
the image source module comprises at least one of a receiver,
transceiver, and transmitter.
19. The EMS device of claim 16, further comprising: an input device
configured to receive input data and to communicate the input data
to the processor.
20. An electromechanical systems (EMS) device, comprising: a
substrate; a stationary electrode over the substrate; a movable
electrode over the stationary electrode and configured to move to
three or more positions across a gap by electrostatic actuation
between the movable electrode and the stationary electrode; and
means for changing the stiffness of the EMS device connected to a
surface of the EMS device, wherein the changing stiffness means is
configured to contact another surface of the EMS device at one of
the positions across the gap, and wherein at least one of the
surfaces in contact with the changing stiffness means is
non-rigid.
21. The EMS device of claim 20, further comprising: means for
supporting the movable electrode over the substrate; and means for
tethering the movable electrode to the supporting means and
symmetrically disposed around the edges of the movable electrode,
wherein the changing stiffness means is connected to the tethering
means.
22. The EMS device of claim 20, wherein the changing stiffness
means is connected to a surface of the movable electrode facing the
stationary electrode.
23. The EMS device of claim 20, wherein the changing stiffness
means is connected to a surface of the substrate facing the movable
electrode.
24. The EMS device of claim 20, wherein the EMS device is part of
an analog interferometric modulator.
25. The EMS device of claim 20, wherein the changing stiffness
means has a height greater than about 20 nm.
26. A method of manufacturing an electromechanical systems (EMS)
device, comprising: providing a substrate; forming a stationary
electrode over the substrate; forming a movable electrode over the
stationary electrode, wherein the movable electrode is configured
to move to three or more positions across a gap by electrostatic
actuation between the movable electrode and the stationary
electrode; and forming a protrusion on a surface of the EMS device,
wherein the protrusion is configured to change the stiffness of the
EMS device when in contact with another surface of the EMS device
at one of the positions across the gap, and wherein at least one of
the surfaces in contact with the protrusion is non-rigid.
27. The method of claim 26, further comprising: forming a plurality
of tethers symmetrically disposed around the edges of the movable
electrode, wherein the protrusion is part of a plurality of
protrusions and each of the protrusions is connected to each of the
tethers.
28. The method of claim 26, wherein the protrusion is connected to
a surface of the movable electrode facing the stationary
electrode.
29. The method of claim 26, wherein the protrusion is connected to
a surface of the substrate facing the movable electrode.
30. The method of claim 26, wherein the protrusion has a height
greater than about 20 nm.
Description
TECHNICAL FIELD
[0001] This disclosure relates to electromechanical systems (EMS)
and devices and more particularly to engineered structures for
stabilizing movable components in interferometric modulators
(IMODs).
DESCRIPTION OF THE RELATED TECHNOLOGY
[0002] Electromechanical systems (EMS) include devices having
electrical and mechanical elements, actuators, transducers,
sensors, optical components such as mirrors and optical films, and
electronics. EMS devices or elements can be manufactured at a
variety of scales including, but not limited to, microscales and
nanoscales. For example, microelectromechanical systems (MEMS)
devices can include structures having sizes ranging from about a
micron to hundreds of microns or more. Nanoelectromechanical
systems (NEMS) devices can include structures having sizes smaller
than a micron including, for example, sizes smaller than several
hundred nanometers. Electromechanical elements may be created using
deposition, etching, lithography, and/or other micromachining
processes that etch away parts of substrates and/or deposited
material layers, or that add layers to form electrical and
electromechanical devices.
[0003] One type of EMS device is called an interferometric
modulator (IMOD). The term IMOD or interferometric light modulator
refers to a device that selectively absorbs and/or reflects light
using the principles of optical interference. In some
implementations, an IMOD display element may include a pair of
conductive plates, one or both of which may be transparent and/or
reflective, wholly or in part, and capable of relative motion upon
application of an appropriate electrical signal. For example, one
plate may include a stationary layer deposited over, on or
supported by a substrate and the other plate may include a
reflective membrane separated from the stationary layer by an air
gap. The position of one plate in relation to another can change
the optical interference of light incident on the IMOD display
element. IMOD-based display devices have a wide range of
applications, and are anticipated to be used in improving existing
products and creating new products, especially those with display
capabilities.
[0004] Many EMS and MEMS devices apply a voltage to generate an
electrostatic attraction between two electrodes to cause one
electrode to move in relation to the other electrode. The positions
of one or both of the electrodes can become unstable as the
electrostatic force between the electrodes increases quadratically
with decreasing distance between the electrodes. Structures or
protrusions can be engineered and connected to portions of the EMS
or MEMS device to stabilize the range of motion in the EMS or MEMS
device.
SUMMARY
[0005] The systems, methods and devices of this disclosure each
have several innovative aspects, no single one of which is solely
responsible for the desirable attributes disclosed herein.
[0006] One innovative aspect of the subject matter described in
this disclosure can be implemented in an electromechanical systems
(EMS) device. The EMS device can include a substrate; a stationary
electrode over the substrate; a movable electrode over the
stationary electrode and configured to move to three or more
positions across a gap by electrostatic actuation between the
movable electrode and the stationary electrode; and a protrusion
connected to a surface of the EMS device. The protrusion is
configured to change the stiffness of the EMS device when in
contact with another surface of the EMS device at one of the
positions across the gap, where at least one of the surfaces in
contact with the protrusion is non-rigid.
[0007] In some implementations, the EMS device can further include
a plurality of tethers symmetrically disposed around the edges of
the movable electrode, where the protrusion is part of a plurality
of protrusions and each of the protrusions is connected to each of
the tethers. In some implementations, the protrusion is connected
to a surface of the movable electrode facing the stationary
electrode. In some implementations, the protrusion is connected to
a surface of the substrate facing the movable electrode. In some
implementations, the EMS device is an optical device. The EMS
device may be part of an analog interferometric modulator (AIMOD).
In some implementations, the protrusion has a height greater than
about 20 nm. In some implementations, the protrusion is part of a
plurality of protrusions, where each of the protrusions has a
different height.
[0008] Another innovative aspect of the subject matter described in
this disclosure can be implemented in an electromechanical systems
(EMS) device. The EMS device can include a substrate; a stationary
electrode over the substrate; a movable electrode over the
stationary electrode and configured to move to three or more
positions across a gap by electrostatic actuation between the
movable electrode and the stationary electrode; and means for
changing the stiffness of the EMS device connected to a surface of
the EMS device. The changing stiffness means is configured to
contact another surface of the EMS device at one of the positions
across the gap, where at least one of the surfaces in contact with
the changing stiffness means is non-rigid.
[0009] In some implementations, the EMS device can further include
means for supporting the movable electrode over the substrate; and
means for tethering the movable electrode to the supporting means
and symmetrically disposed around the edges of the movable
electrode, where the changing stiffness means is connected to
tethering means. In some implementations, the changing stiffness
means is connected to a surface of the movable electrode facing the
stationary electrode. In some implementations, the changing
stiffness means is connected to a surface of the substrate facing
the movable electrode. In some implementations, the changing
stiffness means has a height greater than about 20 nm.
[0010] Another innovative aspect of the subject matter described in
this disclosure can be implemented in a method of manufacturing an
electromechanical systems (EMS) device. The method can include
providing a substrate; forming a stationary electrode over the
substrate; forming a movable electrode over the stationary
electrode, where the movable electrode is configured to move to
three or more positions across a gap by electrostatic actuation
between the movable electrode and the stationary electrode; and
forming a protrusion on a surface of the EMS device. The protrusion
on the surface of the EMS device can be configured to change the
stiffness of the EMS device when in contact with another surface of
the EMS device at one of the positions across the gap, where at
least one of the surfaces in contact with the protrusion is
non-rigid.
[0011] In some implementations, the method can further include
forming a plurality of tethers symmetrically disposed around the
edges of the movable electrode, where the protrusion is part of a
plurality of protrusions and each of the protrusions is connected
to each of the tethers. In some implementations, the protrusion is
connected to a surface of the movable electrode facing the
stationary electrode. In some implementations, the protrusion is
connected to a surface of the substrate facing the movable
electrode. In some implementations, the protrusion has a height
greater than about 20 nm.
[0012] Details of one or more implementations of the subject matter
described in this disclosure are set forth in the accompanying
drawings and the description below. Although the examples provided
in this disclosure are primarily described in terms of EMS and
MEMS-based displays the concepts provided herein may apply to other
types of displays such as liquid crystal displays (LCDs), organic
light-emitting diode ("OLED") displays, and field emission
displays. Other features, aspects, and advantages will become
apparent from the description, the drawings and the claims. Note
that the relative dimensions of the following figures may not be
drawn to scale.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an isometric view illustration depicting two
adjacent interferometric modulator (IMOD) display elements in a
series or array of display elements of an IMOD display device.
[0014] FIG. 2 is a system block diagram illustrating an electronic
device incorporating an IMOD-based display including a three
element by three element array of IMOD display elements.
[0015] FIGS. 3A-3E are cross-sectional illustrations of varying
implementations of IMOD display elements.
[0016] FIG. 4 is a flow diagram illustrating a manufacturing
process for an IMOD display or display element.
[0017] FIGS. 5A-5E are cross-sectional illustrations of various
stages in a process of making an IMOD display or display
element.
[0018] FIGS. 6A and 6B are schematic exploded partial perspective
views of a portion of an electromechanical systems (EMS) package
including an array of EMS elements and a backplate.
[0019] FIG. 7 is an example of a graph illustrating deflection of a
movable electrode as a function of applied voltage.
[0020] FIG. 8 is an example of a color spectrum illustrating the
stable range and black state along a gap distance in an optical EMS
device.
[0021] FIG. 9 is a perspective view of an example of an EMS device
having a movable electrode and a stationary electrode with a gap
therebetween.
[0022] FIG. 10A shows a perspective top view of an example of a
movable electrode of an EMS device having a plurality of
protrusions.
[0023] FIG. 10B shows a perspective bottom view of an example of
the movable electrode of the EMS device in FIG. 10A.
[0024] FIG. 10C shows a perspective bottom view of an example of a
movable electrode of an EMS device having a plurality of
protrusions on the movable electrode.
[0025] FIG. 10D shows an example of a cross-sectional schematic
view of an EMS device with at least one protrusion on the substrate
making contact with one of the tethers.
[0026] FIGS. 11A-11E are cross-sectional illustrations of various
stages in a process of manufacturing an EMS device having a
plurality of protrusions.
[0027] FIG. 12 is an example of a graph illustrating a hysteresis
curve for a position of a movable electrode as a function of
applied voltage of an EMS device.
[0028] FIG. 13 is a flow diagram illustrating a method of
manufacturing an EMS device.
[0029] FIGS. 14A and 14B are system block diagrams illustrating a
display device that includes a plurality of IMOD display
elements.
[0030] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0031] The following description is directed to certain
implementations for the purposes of describing the innovative
aspects of this disclosure. However, a person having ordinary skill
in the art will readily recognize that the teachings herein can be
applied in a multitude of different ways. The described
implementations may be implemented in any device, apparatus, or
system that can be configured to display an image, whether in
motion (such as video) or stationary (such as still images), and
whether textual, graphical or pictorial. More particularly, it is
contemplated that the described implementations may be included in
or associated with a variety of electronic devices such as, but not
limited to: mobile telephones, multimedia Internet enabled cellular
telephones, mobile television receivers, wireless devices,
smartphones, Bluetooth.RTM. devices, personal data assistants
(PDAs), wireless electronic mail receivers, hand-held or portable
computers, netbooks, notebooks, smartbooks, tablets, printers,
copiers, scanners, facsimile devices, global positioning system
(GPS) receivers/navigators, cameras, digital media players (such as
MP3 players), camcorders, game consoles, wrist watches, clocks,
calculators, television monitors, flat panel displays, electronic
reading devices (e.g., e-readers), computer monitors, auto displays
(including odometer and speedometer displays, etc.), cockpit
controls and/or displays, camera view displays (such as the display
of a rear view camera in a vehicle), electronic photographs,
electronic billboards or signs, projectors, architectural
structures, microwaves, refrigerators, stereo systems, cassette
recorders or players, DVD players, CD players, VCRs, radios,
portable memory chips, washers, dryers, washer/dryers, parking
meters, packaging (such as in electromechanical systems (EMS)
applications including microelectromechanical systems (MEMS)
applications, as well as non-EMS applications), aesthetic
structures (such as display of images on a piece of jewelry or
clothing) and a variety of EMS devices. The teachings herein also
can be used in non-display applications such as, but not limited
to, electronic switching devices, radio frequency filters, sensors,
accelerometers, gyroscopes, motion-sensing devices, magnetometers,
inertial components for consumer electronics, parts of consumer
electronics products, varactors, liquid crystal devices,
electrophoretic devices, drive schemes, manufacturing processes and
electronic test equipment. Thus, the teachings are not intended to
be limited to the implementations depicted solely in the Figures,
but instead have wide applicability as will be readily apparent to
one having ordinary skill in the art.
[0032] Some implementations described herein relate to EMS devices
with one or more protrusions connected to a surface of the EMS
device. The EMS device can include a substrate, a stationary
electrode over the substrate, and a movable electrode over the
stationary electrode. The movable electrode can be configured to
move to three or more positions across a gap by electrostatic
actuation between the movable electrode and the stationary
electrode. When the protrusions contact another surface of the EMS
device at one of the positions across the gap, the protrusions can
change the stiffness of the EMS device where at least one of the
surfaces in contact with the one or more protrusions is non-rigid.
The protrusions can each have a height greater than about 20 nm,
such as between about 20 nm and about 4000 nm, and such as between
about 100 nm and 200 nm. The EMS device can include a plurality of
tethers symmetrically disposed around the edges of the movable
electrode. Each of the protrusions can be connected to each of the
tethers, or connected to a surface of the movable electrode facing
the stationary electrode.
[0033] Particular implementations of the subject matter described
in this disclosure can be implemented to realize one or more of the
following potential advantages. Protrusions on a surface of the EMS
device can contact another surface of the EMS device to change the
overall stiffness of the EMS device during actuation when at least
one of the surfaces in contact with the protrusions is non-rigid,
leading to a higher restoring force to counter the effects of
snap-through. As a result, the protrusions can provide at least an
additional stable region of operation. In fact, multiple
protrusions of different heights can provide further stable regions
of operation. With additional stable regions of operation, some EMS
devices including optical EMS devices can provide additional stable
color ranges, including black. Furthermore, the protrusions also
can provide larger restoring forces to overcome the effects of
stiction between the movable electrode and the stationary electrode
when the protrusions are in contact.
[0034] An example of a suitable EMS or MEMS device or apparatus, to
which the described implementations may apply, is a reflective
display device. Reflective display devices can incorporate
interferometric modulator (IMOD) display elements that can be
implemented to selectively absorb and/or reflect light incident
thereon using principles of optical interference. IMOD display
elements can include a partial optical absorber, a reflector that
is movable with respect to the absorber, and an optical resonant
cavity defined between the absorber and the reflector. In some
implementations, the reflector can be moved to two or more
different positions, which can change the size of the optical
resonant cavity and thereby affect the reflectance of the IMOD. The
reflectance spectra of IMOD display elements can create fairly
broad spectral bands that can be shifted across the visible
wavelengths to generate different colors. The position of the
spectral band can be adjusted by changing the thickness of the
optical resonant cavity. One way of changing the optical resonant
cavity is by changing the position of the reflector with respect to
the absorber.
[0035] FIG. 1 is an isometric view illustration depicting two
adjacent interferometric modulator (IMOD) display elements in a
series or array of display elements of an IMOD display device. The
IMOD display device includes one or more interferometric EMS, such
as MEMS, display elements. In these devices, the interferometric
MEMS display elements can be configured in either a bright or dark
state. In the bright ("relaxed," "open" or "on," etc.) state, the
display element reflects a large portion of incident visible light.
Conversely, in the dark ("actuated," "closed" or "off," etc.)
state, the display element reflects little incident visible light.
MEMS display elements can be configured to reflect predominantly at
particular wavelengths of light allowing for a color display in
addition to black and white. In some implementations, by using
multiple display elements, different intensities of color primaries
and shades of gray can be achieved.
[0036] The IMOD display device can include an array of IMOD display
elements which may be arranged in rows and columns. Each display
element in the array can include at least a pair of reflective and
semi-reflective layers, such as a movable reflective layer (i.e., a
movable layer, also referred to as a mechanical layer) and a fixed
partially reflective layer (i.e., a stationary layer), positioned
at a variable and controllable distance from each other to form an
air gap (also referred to as an optical gap, cavity or optical
resonant cavity). The movable reflective layer may be moved between
at least two positions. For example, in a first position, i.e., a
relaxed position, the movable reflective layer can be positioned at
a distance from the fixed partially reflective layer. In a second
position, i.e., an actuated position, the movable reflective layer
can be positioned more closely to the partially reflective layer.
Incident light that reflects from the two layers can interfere
constructively and/or destructively depending on the position of
the movable reflective layer and the wavelength(s) of the incident
light, producing either an overall reflective or non-reflective
state for each display element. In some implementations, the
display element may be in a reflective state when unactuated,
reflecting light within the visible spectrum, and may be in a dark
state when actuated, absorbing and/or destructively interfering
light within the visible range. In some other implementations,
however, an IMOD display element may be in a dark state when
unactuated, and in a reflective state when actuated. In some
implementations, the introduction of an applied voltage can drive
the display elements to change states. In some other
implementations, an applied charge can drive the display elements
to change states.
[0037] The depicted portion of the array in FIG. 1 includes two
adjacent interferometric MEMS display elements in the form of IMOD
display elements 12. In the display element 12 on the right (as
illustrated), the movable reflective layer 14 is illustrated in an
actuated position near, adjacent or touching the optical stack 16.
The voltage V.sub.bias applied across the display element 12 on the
right is sufficient to move and also maintain the movable
reflective layer 14 in the actuated position. In the display
element 12 on the left (as illustrated), a movable reflective layer
14 is illustrated in a relaxed position at a distance (which may be
predetermined based on design parameters) from an optical stack 16,
which includes a partially reflective layer. The voltage V.sub.0
applied across the display element 12 on the left is insufficient
to cause actuation of the movable reflective layer 14 to an
actuated position such as that of the display element 12 on the
right.
[0038] In FIG. 1, the reflective properties of IMOD display
elements 12 are generally illustrated with arrows indicating light
13 incident upon the IMOD display elements 12, and light 15
reflecting from the display element 12 on the left. Most of the
light 13 incident upon the display elements 12 may be transmitted
through the transparent substrate 20, toward the optical stack 16.
A portion of the light incident upon the optical stack 16 may be
transmitted through the partially reflective layer of the optical
stack 16, and a portion will be reflected back through the
transparent substrate 20. The portion of light 13 that is
transmitted through the optical stack 16 may be reflected from the
movable reflective layer 14, back toward (and through) the
transparent substrate 20. Interference (constructive and/or
destructive) between the light reflected from the partially
reflective layer of the optical stack 16 and the light reflected
from the movable reflective layer 14 will determine in part the
intensity of wavelength(s) of light 15 reflected from the display
element 12 on the viewing or substrate side of the device. In some
implementations, the transparent substrate 20 can be a glass
substrate (sometimes referred to as a glass plate or panel). The
glass substrate may be or include, for example, a borosilicate
glass, a soda lime glass, quartz, Pyrex, or other suitable glass
material. In some implementations, the glass substrate may have a
thickness of 0.3, 0.5 or 0.7 millimeters, although in some
implementations the glass substrate can be thicker (such as tens of
millimeters) or thinner (such as less than 0.3 millimeters). In
some implementations, a non-glass substrate can be used, such as a
polycarbonate, acrylic, polyethylene terephthalate (PET) or
polyether ether ketone (PEEK) substrate. In such an implementation,
the non-glass substrate will likely have a thickness of less than
0.7 millimeters, although the substrate may be thicker depending on
the design considerations. In some implementations, a
non-transparent substrate, such as a metal foil or stainless
steel-based substrate can be used. For example, a
reverse-IMOD-based display, which includes a fixed reflective layer
and a movable layer which is partially transmissive and partially
reflective, may be configured to be viewed from the opposite side
of a substrate as the display elements 12 of FIG. 1 and may be
supported by a non-transparent substrate.
[0039] The optical stack 16 can include a single layer or several
layers. The layer(s) can include one or more of an electrode layer,
a partially reflective and partially transmissive layer, and a
transparent dielectric layer. In some implementations, the optical
stack 16 is electrically conductive, partially transparent and
partially reflective, and may be fabricated, for example, by
depositing one or more of the above layers onto a transparent
substrate 20. The electrode layer can be formed from a variety of
materials, such as various metals, for example indium tin oxide
(ITO). The partially reflective layer can be formed from a variety
of materials that are partially reflective, such as various metals
(e.g., chromium and/or molybdenum), semiconductors, and
dielectrics. The partially reflective layer can be formed of one or
more layers of materials, and each of the layers can be formed of a
single material or a combination of materials. In some
implementations, certain portions of the optical stack 16 can
include a single semi-transparent thickness of metal or
semiconductor which serves as both a partial optical absorber and
electrical conductor, while different, electrically more conductive
layers or portions (e.g., of the optical stack 16 or of other
structures of the display element) can serve to bus signals between
IMOD display elements. The optical stack 16 also can include one or
more insulating or dielectric layers covering one or more
conductive layers or an electrically conductive/partially
absorptive layer.
[0040] In some implementations, at least some of the layer(s) of
the optical stack 16 can be patterned into parallel strips, and may
form row electrodes in a display device as described further below.
As will be understood by one having ordinary skill in the art, the
term "patterned" is used herein to refer to masking as well as
etching processes. In some implementations, a highly conductive and
reflective material, such as aluminum (Al), may be used for the
movable reflective layer 14, and these strips may form column
electrodes in a display device. The movable reflective layer 14 may
be formed as a series of parallel strips of a deposited metal layer
or layers (orthogonal to the row electrodes of the optical stack
16) to form columns deposited on top of supports, such as the
illustrated posts 18, and an intervening sacrificial material
located between the posts 18. When the sacrificial material is
etched away, a defined gap 19, or optical cavity, can be formed
between the movable reflective layer 14 and the optical stack 16.
In some implementations, the spacing between posts 18 may be
approximately 1-1000 .mu.m, while the gap 19 may be approximately
less than 10,000 Angstroms (.ANG.).
[0041] In some implementations, each IMOD display element, whether
in the actuated or relaxed state, can be considered as a capacitor
formed by the fixed and moving reflective layers. When no voltage
is applied, the movable reflective layer 14 remains in a
mechanically relaxed state, as illustrated by the display element
12 on the left in FIG. 1, with the gap 19 between the movable
reflective layer 14 and optical stack 16. However, when a potential
difference, i.e., a voltage, is applied to at least one of a
selected row and column, the capacitor formed at the intersection
of the row and column electrodes at the corresponding display
element becomes charged, and electrostatic forces pull the
electrodes together. If the applied voltage exceeds a threshold,
the movable reflective layer 14 can deform and move near or against
the optical stack 16. A dielectric layer (not shown) within the
optical stack 16 may prevent shorting and control the separation
distance between the layers 14 and 16, as illustrated by the
actuated display element 12 on the right in FIG. 1. The behavior
can be the same regardless of the polarity of the applied potential
difference. Though a series of display elements in an array may be
referred to in some instances as "rows" or "columns," a person
having ordinary skill in the art will readily understand that
referring to one direction as a "row" and another as a "column" is
arbitrary. Restated, in some orientations, the rows can be
considered columns, and the columns considered to be rows. In some
implementations, the rows may be referred to as "common" lines and
the columns may be referred to as "segment" lines, or vice versa.
Furthermore, the display elements may be evenly arranged in
orthogonal rows and columns (an "array"), or arranged in non-linear
configurations, for example, having certain positional offsets with
respect to one another (a "mosaic"). The terms "array" and "mosaic"
may refer to either configuration. Thus, although the display is
referred to as including an "array" or "mosaic," the elements
themselves need not be arranged orthogonally to one another, or
disposed in an even distribution, in any instance, but may include
arrangements having asymmetric shapes and unevenly distributed
elements.
[0042] FIG. 2 is a system block diagram illustrating an electronic
device incorporating an IMOD-based display including a three
element by three element array of IMOD display elements. The
electronic device includes a processor 21 that may be configured to
execute one or more software modules. In addition to executing an
operating system, the processor 21 may be configured to execute one
or more software applications, including a web browser, a telephone
application, an email program, or any other software
application.
[0043] The processor 21 can be configured to communicate with an
array driver 22. The array driver 22 can include a row driver
circuit 24 and a column driver circuit 26 that provide signals to,
for example a display array or panel 30. The cross section of the
IMOD display device illustrated in FIG. 1 is shown by the lines 1-1
in FIG. 2. Although FIG. 2 illustrates a 3.times.3 array of IMOD
display elements for the sake of clarity, the display array 30 may
contain a very large number of IMOD display elements, and may have
a different number of IMOD display elements in rows than in
columns, and vice versa.
[0044] The details of the structure of IMOD displays and display
elements may vary widely. FIGS. 3A-3E are cross-sectional
illustrations of varying implementations of IMOD display elements.
FIG. 3A is a cross-sectional illustration of an IMOD display
element, where a strip of metal material is deposited on supports
18 extending generally orthogonally from the substrate 20 forming
the movable reflective layer 14. In FIG. 3B, the movable reflective
layer 14 of each IMOD display element is generally square or
rectangular in shape and attached to supports at or near the
corners, on tethers 32. In FIG. 3C, the movable reflective layer 14
is generally square or rectangular in shape and suspended from a
deformable layer 34, which may include a flexible metal. The
deformable layer 34 can connect, directly or indirectly, to the
substrate 20 around the perimeter of the movable reflective layer
14. These connections are herein referred to as implementations of
"integrated" supports or support posts 18. The implementation shown
in FIG. 3C has additional benefits deriving from the decoupling of
the optical functions of the movable reflective layer 14 from its
mechanical functions, the latter of which are carried out by the
deformable layer 34. This decoupling allows the structural design
and materials used for the movable reflective layer 14 and those
used for the deformable layer 34 to be optimized independently of
one another.
[0045] FIG. 3D is another cross-sectional illustration of an IMOD
display element, where the movable reflective layer 14 includes a
reflective sub-layer 14a. The movable reflective layer 14 rests on
a support structure, such as support posts 18. The support posts 18
provide separation of the movable reflective layer 14 from the
lower stationary electrode, which can be part of the optical stack
16 in the illustrated IMOD display element. For example, a gap 19
is formed between the movable reflective layer 14 and the optical
stack 16, when the movable reflective layer 14 is in a relaxed
position. The movable reflective layer 14 also can include a
conductive layer 14c, which may be configured to serve as an
electrode, and a support layer 14b. In this example, the conductive
layer 14c is disposed on one side of the support layer 14b, distal
from the substrate 20, and the reflective sub-layer 14a is disposed
on the other side of the support layer 14b, proximal to the
substrate 20. In some implementations, the reflective sub-layer 14a
can be conductive and can be disposed between the support layer 14b
and the optical stack 16. The support layer 14b can include one or
more layers of a dielectric material, for example, silicon
oxynitride (SiON) or silicon dioxide (SiO.sub.2). In some
implementations, the support layer 14b can be a stack of layers,
such as, for example, a SiO.sub.2/SiON/SiO.sub.2 tri-layer stack.
Either or both of the reflective sub-layer 14a and the conductive
layer 14c can include, for example, an aluminum (Al) alloy with
about 0.5% copper (Cu), or another reflective metallic material.
Employing conductive layers 14a and 14c above and below the
dielectric support layer 14b can balance stresses and provide
enhanced conduction. In some implementations, the reflective
sub-layer 14a and the conductive layer 14c can be formed of
different materials for a variety of design purposes, such as
achieving specific stress profiles within the movable reflective
layer 14.
[0046] As illustrated in FIG. 3D, some implementations also can
include a black mask structure 23, or dark film layers. The black
mask structure 23 can be formed in optically inactive regions (such
as between display elements or under the support posts 18) to
absorb ambient or stray light. The black mask structure 23 also can
improve the optical properties of a display device by inhibiting
light from being reflected from or transmitted through inactive
portions of the display, thereby increasing the contrast ratio.
Additionally, at least some portions of the black mask structure 23
can be conductive and be configured to function as an electrical
bussing layer. In some implementations, the row electrodes can be
connected to the black mask structure 23 to reduce the resistance
of the connected row electrode. The black mask structure 23 can be
formed using a variety of methods, including deposition and
patterning techniques. The black mask structure 23 can include one
or more layers. In some implementations, the black mask structure
23 can be an etalon or interferometric stack structure. For
example, in some implementations, the interferometric stack black
mask structure 23 includes a molybdenum-chromium (MoCr) layer that
serves as an optical absorber, an SiO.sub.2 layer, and an aluminum
alloy that serves as a reflector and a bussing layer, with a
thickness in the range of about 30-80 .ANG., 500-1000 .ANG., and
500-6000 .ANG., respectively. The one or more layers can be
patterned using a variety of techniques, including photolithography
and dry etching, including, for example, tetrafluoromethane (or
carbon tetrafluoride, CF.sub.4) and/or oxygen (O.sub.2) for the
MoCr and SiO.sub.2 layers and chlorine (Cl.sub.2) and/or boron
trichloride (BCl.sub.3) for the aluminum alloy layer. In such
interferometric stack black mask structures 23, the conductive
absorbers can be used to transmit or bus signals between lower,
stationary electrodes in the optical stack 16 of each row or
column. In some implementations, a spacer layer 35 can serve to
generally electrically isolate electrodes (or conductors) in the
optical stack 16 (such as the absorber layer 16a) from the
conductive layers in the black mask structure 23.
[0047] FIG. 3E is another cross-sectional illustration of an IMOD
display element, where the movable reflective layer 14 is
self-supporting. While FIG. 3D illustrates support posts 18 that
are structurally and/or materially distinct from the movable
reflective layer 14, the implementation of FIG. 3E includes support
posts that are integrated with the movable reflective layer 14. In
such an implementation, the movable reflective layer 14 contacts
the underlying optical stack 16 at multiple locations, and the
curvature of the movable reflective layer 14 provides sufficient
support that the movable reflective layer 14 returns to the
unactuated position of FIG. 3E when the voltage across the IMOD
display element is insufficient to cause actuation. In this way,
the portion of the movable reflective layer 14 that curves or bends
down to contact the substrate or optical stack 16 may be considered
an "integrated" support post. One implementation of the optical
stack 16, which may contain a plurality of several different
layers, is shown here for clarity including an optical absorber
16a, and a dielectric 16b. In some implementations, the optical
absorber 16a may serve both as a stationary electrode and as a
partially reflective layer. In some implementations, the optical
absorber 16a can be an order of magnitude thinner than the movable
reflective layer 14. In some implementations, the optical absorber
16a is thinner than the reflective sub-layer 14a.
[0048] In implementations such as those shown in FIGS. 3A-3E, the
IMOD display elements form a part of a direct-view device, in which
images can be viewed from the front side of the transparent
substrate 20, which in this example is the side opposite to that
upon which the IMOD display elements are formed. In these
implementations, the back portions of the device (that is, any
portion of the display device behind the movable reflective layer
14, including, for example, the deformable layer 34 illustrated in
FIG. 3C) can be configured and operated upon without impacting or
negatively affecting the image quality of the display device,
because the reflective layer 14 optically shields those portions of
the device. For example, in some implementations a bus structure
(not illustrated) can be included behind the movable reflective
layer 14 that provides the ability to separate the optical
properties of the modulator from the electromechanical properties
of the modulator, such as voltage addressing and the movements that
result from such addressing.
[0049] FIG. 4 is a flow diagram illustrating a manufacturing
process 80 for an IMOD display or display element. FIGS. 5A-5E are
cross-sectional illustrations of various stages in the
manufacturing process 80 for making an IMOD display or display
element. In some implementations, the manufacturing process 80 can
be implemented to manufacture one or more EMS devices, such as IMOD
displays or display elements. The manufacture of such an EMS device
also can include other blocks not shown in FIG. 4. The process 80
begins at block 82 with the formation of the optical stack 16 over
the substrate 20. FIG. 5A illustrates such an optical stack 16
formed over the substrate 20. The substrate 20 may be a transparent
substrate such as glass or plastic such as the materials discussed
above with respect to FIG. 1. The substrate 20 may be flexible or
relatively stiff and unbending, and may have been subjected to
prior preparation processes, such as cleaning, to facilitate
efficient formation of the optical stack 16. As discussed above,
the optical stack 16 can be electrically conductive, partially
transparent, partially reflective, and partially absorptive, and
may be fabricated, for example, by depositing one or more layers
having the desired properties onto the transparent substrate
20.
[0050] In FIG. 5A, the optical stack 16 includes a multilayer
structure having sub-layers 16a and 16b, although more or fewer
sub-layers may be included in some other implementations. In some
implementations, one of the sub-layers 16a and 16b can be
configured with both optically absorptive and electrically
conductive properties, such as the combined conductor/absorber
sub-layer 16a. In some implementations, one of the sub-layers 16a
and 16b can include molybdenum-chromium (molychrome or MoCr), or
other materials with a suitable complex refractive index.
Additionally, one or more of the sub-layers 16a and 16b can be
patterned into parallel strips, and may form row electrodes in a
display device. Such patterning can be performed by a masking and
etching process or another suitable process known in the art. In
some implementations, one of the sub-layers 16a and 16b can be an
insulating or dielectric layer, such as an upper sub-layer 16b that
is deposited over one or more underlying metal and/or oxide layers
(such as one or more reflective and/or conductive layers). In
addition, the optical stack 16 can be patterned into individual and
parallel strips that form the rows of the display. In some
implementations, at least one of the sub-layers of the optical
stack, such as the optically absorptive layer, may be quite thin
(e.g., relative to other layers depicted in this disclosure), even
though the sub-layers 16a and 16b are shown somewhat thick in FIGS.
5A-5E.
[0051] The process 80 continues at block 84 with the formation of a
sacrificial layer 25 over the optical stack 16. Because the
sacrificial layer 25 is later removed (see block 90) to form the
cavity 19, the sacrificial layer 25 is not shown in the resulting
IMOD display elements. FIG. 5B illustrates a partially fabricated
device including a sacrificial layer 25 formed over the optical
stack 16. The formation of the sacrificial layer 25 over the
optical stack 16 may include deposition of a xenon difluoride
(XeF.sub.2)-etchable material such as molybdenum (Mo) or amorphous
silicon (Si), in a thickness selected to provide, after subsequent
removal, a gap or cavity 19 (see also FIG. 5E) having a desired
design size. Deposition of the sacrificial material may be carried
out using deposition techniques such as physical vapor deposition
(PVD, which includes many different techniques, such as
sputtering), plasma-enhanced chemical vapor deposition (PECVD),
thermal chemical vapor deposition (thermal CVD), or
spin-coating.
[0052] The process 80 continues at block 86 with the formation of a
support structure such as a support post 18. The formation of the
support post 18 may include patterning the sacrificial layer 25 to
form a support structure aperture, then depositing a material (such
as a polymer or an inorganic material, like silicon oxide) into the
aperture to form the support post 18, using a deposition method
such as PVD, PECVD, thermal CVD, or spin-coating. In some
implementations, the support structure aperture formed in the
sacrificial layer can extend through both the sacrificial layer 25
and the optical stack 16 to the underlying substrate 20, so that
the lower end of the support post 18 contacts the substrate 20.
Alternatively, as depicted in FIG. 5C, the aperture formed in the
sacrificial layer 25 can extend through the sacrificial layer 25,
but not through the optical stack 16. For example, FIG. 5E
illustrates the lower ends of the support posts 18 in contact with
an upper surface of the optical stack 16. The support post 18, or
other support structures, may be formed by depositing a layer of
support structure material over the sacrificial layer 25 and
patterning portions of the support structure material located away
from apertures in the sacrificial layer 25. The support structures
may be located within the apertures, as illustrated in FIG. 5C, but
also can extend at least partially over a portion of the
sacrificial layer 25. As noted above, the patterning of the
sacrificial layer 25 and/or the support posts 18 can be performed
by a masking and etching process, but also may be performed by
alternative patterning methods.
[0053] The process 80 continues at block 88 with the formation of a
movable reflective layer or membrane such as the movable reflective
layer 14 illustrated in FIG. 5D. The movable reflective layer 14
may be formed by employing one or more deposition steps, including,
for example, reflective layer (such as aluminum, aluminum alloy, or
other reflective materials) deposition, along with one or more
patterning, masking and/or etching steps. The movable reflective
layer 14 can be patterned into individual and parallel strips that
form, for example, the columns of the display. The movable
reflective layer 14 can be electrically conductive, and referred to
as an electrically conductive layer. In some implementations, the
movable reflective layer 14 may include a plurality of sub-layers
14a, 14b and 14c as shown in FIG. 5D. In some implementations, one
or more of the sub-layers, such as sub-layers 14a and 14c, may
include highly reflective sub-layers selected for their optical
properties, and another sub-layer 14b may include a mechanical
sub-layer selected for its mechanical properties. In some
implementations, the mechanical sub-layer may include a dielectric
material. Since the sacrificial layer 25 is still present in the
partially fabricated IMOD display element formed at block 88, the
movable reflective layer 14 is typically not movable at this stage.
A partially fabricated IMOD display element that contains a
sacrificial layer 25 also may be referred to herein as an
"unreleased" IMOD.
[0054] The process 80 continues at block 90 with the formation of a
cavity 19. The cavity 19 may be formed by exposing the sacrificial
material 25 (deposited at block 84) to an etchant. For example, an
etchable sacrificial material such as Mo or amorphous Si may be
removed by dry chemical etching by exposing the sacrificial layer
25 to a gaseous or vaporous etchant, such as vapors derived from
solid XeF.sub.2 for a period of time that is effective to remove
the desired amount of material. The sacrificial material is
typically selectively removed relative to the structures
surrounding the cavity 19. Other etching methods, such as wet
etching and/or plasma etching, also may be used. Since the
sacrificial layer 25 is removed during block 90, the movable
reflective layer 14 is typically movable after this stage. After
removal of the sacrificial material 25, the resulting fully or
partially fabricated IMOD display element may be referred to herein
as a "released" IMOD.
[0055] In some implementations, the packaging of an EMS component
or device, such as an IMOD-based display, can include a backplate
(alternatively referred to as a backplane, back glass or recessed
glass) which can be configured to protect the EMS components from
damage (such as from mechanical interference or potentially
damaging substances). The backplate also can provide structural
support for a wide range of components, including but not limited
to driver circuitry, processors, memory, interconnect arrays, vapor
barriers, product housing, and the like. In some implementations,
the use of a backplate can facilitate integration of components and
thereby reduce the volume, weight, and/or manufacturing costs of a
portable electronic device.
[0056] FIGS. 6A and 6B are schematic exploded partial perspective
views of a portion of an EMS package 91 including an array 36 of
EMS elements and a backplate 92. FIG. 6A is shown with two corners
of the backplate 92 cut away to better illustrate certain portions
of the backplate 92, while FIG. 6B is shown without the corners cut
away. The EMS array 36 can include a substrate 20, support posts
18, and a movable layer 14. In some implementations, the EMS array
36 can include an array of IMOD display elements with one or more
optical stack portions 16 on a transparent substrate, and the
movable layer 14 can be implemented as a movable reflective
layer.
[0057] The backplate 92 can be essentially planar or can have at
least one contoured surface (e.g., the backplate 92 can be formed
with recesses and/or protrusions). The backplate 92 may be made of
any suitable material, whether transparent or opaque, conductive or
insulating. Suitable materials for the backplate 92 include, but
are not limited to, glass, plastic, ceramics, polymers, laminates,
metals, metal foils, Kovar and plated Kovar.
[0058] As shown in FIGS. 6A and 6B, the backplate 92 can include
one or more backplate components 94a and 94b, which can be
partially or wholly embedded in the backplate 92. As can be seen in
FIG. 6A, backplate component 94a is embedded in the backplate 92.
As can be seen in FIGS. 6A and 6B, backplate component 94b is
disposed within a recess 93 formed in a surface of the backplate
92. In some implementations, the backplate components 94a and/or
94b can protrude from a surface of the backplate 92. Although
backplate component 94b is disposed on the side of the backplate 92
facing the substrate 20, in other implementations, the backplate
components can be disposed on the opposite side of the backplate
92.
[0059] The backplate components 94a and/or 94b can include one or
more active or passive electrical components, such as transistors,
capacitors, inductors, resistors, diodes, switches, and/or
integrated circuits (ICs) such as a packaged, standard or discrete
IC. Other examples of backplate components that can be used in
various implementations include antennas, batteries, and sensors
such as electrical, touch, optical, or chemical sensors, or
thin-film deposited devices.
[0060] In some implementations, the backplate components 94a and/or
94b can be in electrical communication with portions of the EMS
array 36. Conductive structures such as traces, bumps, posts, or
vias may be formed on one or both of the backplate 92 or the
substrate 20 and may contact one another or other conductive
components to form electrical connections between the EMS array 36
and the backplate components 94a and/or 94b. For example, FIG. 6B
includes one or more conductive vias 96 on the backplate 92 which
can be aligned with electrical contacts 98 extending upward from
the movable layers 14 within the EMS array 36. In some
implementations, the backplate 92 also can include one or more
insulating layers that electrically insulate the backplate
components 94a and/or 94b from other components of the EMS array
36. In some implementations in which the backplate 92 is formed
from vapor-permeable materials, an interior surface of backplate 92
can be coated with a vapor barrier (not shown).
[0061] The backplate components 94a and 94b can include one or more
desiccants which act to absorb any moisture that may enter the EMS
package 91. In some implementations, a desiccant (or other moisture
absorbing materials, such as a getter) may be provided separately
from any other backplate components, for example as a sheet that is
mounted to the backplate 92 (or in a recess formed therein) with
adhesive. Alternatively, the desiccant may be integrated into the
backplate 92. In some other implementations, the desiccant may be
applied directly or indirectly over other backplate components, for
example by spray-coating, screen printing, or any other suitable
method.
[0062] In some implementations, the EMS array 36 and/or the
backplate 92 can include mechanical standoffs 97 to maintain a
distance between the backplate components and the display elements
and thereby prevent mechanical interference between those
components. In the implementation illustrated in FIGS. 6A and 6B,
the mechanical standoffs 97 are formed as posts protruding from the
backplate 92 in alignment with the support posts 18 of the EMS
array 36. Alternatively or in addition, mechanical standoffs, such
as rails or posts, can be provided along the edges of the EMS
package 91.
[0063] Although not illustrated in FIGS. 6A and 6B, a seal can be
provided which partially or completely encircles the EMS array 36.
Together with the backplate 92 and the substrate 20, the seal can
form a protective cavity enclosing the EMS array 36. The seal may
be a semi-hermetic seal, such as a conventional epoxy-based
adhesive. In some other implementations, the seal may be a hermetic
seal, such as a thin film metal weld or a glass frit. In some other
implementations, the seal may include polyisobutylene (PIB),
polyurethane, liquid spin-on glass, solder, polymers, plastics, or
other materials. In some implementations, a reinforced sealant can
be used to form mechanical standoffs.
[0064] In alternate implementations, a seal ring may include an
extension of either one or both of the backplate 92 or the
substrate 20. For example, the seal ring may include a mechanical
extension (not shown) of the backplate 92. In some implementations,
the seal ring may include a separate member, such as an O-ring or
other annular member.
[0065] In some implementations, the EMS array 36 and the backplate
92 are separately formed before being attached or coupled together.
For example, the edge of the substrate 20 can be attached and
sealed to the edge of the backplate 92 as discussed above.
Alternatively, the EMS array 36 and the backplate 92 can be formed
and joined together as the EMS package 91. In some other
implementations, the EMS package 91 can be fabricated in any other
suitable manner, such as by forming components of the backplate 92
over the EMS array 36 by deposition.
[0066] Many MEMS and EMS devices apply a voltage to generate an
electrostatic attraction between two electrodes. The electrostatic
attraction between the two electrodes can induce a nonlinear
electrostatic force. The electrostatic force can increase
quadratically as the distance between the two electrodes
decreases.
[0067] FIG. 7 is an example of a graph illustrating deflection of a
movable electrode as a function of applied voltage. The movable
electrode can be part of a MEMS or EMS device. The equation below
can be used to measure electrostatic force between two
electrodes:
F=(V.sup.2.di-elect cons..sub.0A.sub.E)/(2D.sup.2)
where A.sub.E is the common surface area between the two
electrodes, V is the voltage potential between the two electrodes,
.di-elect cons..sub.0 is the permittivity of free space, and D is
the separate distance between the two electrodes. D=(z.sub.0-d),
and z.sub.0 is the initial separation distance and d is the
deflection distance.
[0068] In the example in FIG. 7, the movable electrode is part of a
MEMS device with a micromirror or mirror plate. Data for the graph
in FIG. 7 was provided in a publication by David M. Burns and
Victor M. Bright, "Nonlinear Flexures for stable deflection of an
electrostatically actuated micromirror," SPIE Vol. 3226, pp.
125-136 (April 2011), the entirety of which is hereby incorporated
by reference. The MEMS device in the Burns publication had a
permittivity of free space, .di-elect cons..sub.0, of
8.854.times.10.sup.-14 F/cm, a common surface area between two
electrodes, A.sub.E, of 5252 .mu.m.sup.2, and an initial electrode
separation, z.sub.0, of 2.09 .mu.m.
[0069] Because electrostatic force is inversely proportional to
separation distance between two electrodes, and increases
quadratically as the separation distance decreases, the position of
one of the electrodes can become unstable as the electrode travels
across the separation distance. For example, after the separation
distance between the electrodes decreases by about one-third, the
relative position of the electrodes can become unstable, and the
electrodes can quickly travel the remaining separation distance.
This phenomenon is called "snap-through," and can limit the useful
range of motion in a MEMS or EMS device.
[0070] Moreover, as the movable electrode tilts by even the
slightest degree, charge can build up in the area of the tilt that
serves as a positively reinforcing mechanism, which results in tilt
instability. The tilt instability may result from any asymmetry in
the MEMS or EMS device, including mismatched tethers, shape of the
electrodes, or uneven initial separation distance. Beyond a certain
critical travel range or tilt angle, which depends on the ratio of
the electrostatic to the mechanical restoring torques, the tilting
becomes unstable and one side or corner of the device will snap
down. These protrusions also can extend the tilt-stable range by
increasing the mechanical restoring torque.
[0071] Some MEMS or EMS devices may include optical devices, such
as IMODs, as discussed earlier herein. A movable electrode can have
a reflective layer configured to move across a gap by electrostatic
attraction toward a stationary electrode with an absorber layer.
The movable electrode can be configured to interferometrically
modulate light of a particular wavelength based at least in part on
the size of the gap. Typically, an IMOD can have a stable range
from an initial electrical gap at about 540 nm (e.g., green) to
about 360 nm (e.g., red). Hence, the IMOD can tune continuously
within the red-green-blue (RGB) color spectrum from about 360 nm to
about 540 nm. In an analog IMOD (AIMOD), the movable electrode with
the reflective layer can be configured to move to three or more
different distances from the stationary electrode with the absorber
layer. In other words, the reflective layer can move and stop at
three or more different positions from the absorber layer.
[0072] However, when the movable electrode exceeds a certain
critical travel range or title angle, the movable electrode may
become unstable and snap-through towards the stationary electrode.
This can create an unstable region for various wavelengths of
light, including black. Some AIMODs try to extend the stable region
of the electrical gap by driving with charge instead of voltage, or
add a capacitor in series. Such configurations of AIMODs are still
subject to tilt instability, however, where even the slightest tilt
in the movable electrode can concentrate electrostatic charge
locally and cause the electrostatic force on the movable electrode
to increase exponentially.
[0073] FIG. 8 is an example of a color spectrum illustrating the
stable range and black state along a gap distance in an optical EMS
device. In some implementations, the optical EMS device can include
an IMOD. The gap distance measured in nanometers represents the
distance from the stationary electrode to the movable electrode. In
some implementations, the movable electrode can include a
reflective layer and the stationary electrode can include an
optical stack with an absorber layer.
[0074] To achieve the desired color gamut (e.g., red-green-blue
color spectrum) the initial gap distance can be chosen to be
between about 400 nm and about 700 nm, such as between about 450 nm
and about 650 nm. For example, in the example in FIG. 8, the
initial gap distance is chosen to be about 540 nm. The initial gap
distance can be chosen so that the desired color gamut is within
the stable range of operation before snap-through.
[0075] As illustrated in the example in FIG. 8, the black state for
the optical EMS device can be outside the stable range. In FIG. 8,
the black state can be between about 100 nm and about 200 nm, such
as about 140 nm. In some implementations, for an optical EMS device
to reach the black state stably, the stable range of the optical
EMS device can be increased.
[0076] FIG. 9 is a perspective view of an example of an EMS device
having a movable electrode and a stationary electrode with a gap
therebetween. The stationary electrode 160 can be formed on a
substrate 200. A plurality of support posts 180 can be disposed
over the stationary electrode 160 and at least proximate to the
corners of the substrate 200. The movable electrode 140 can be
connected to the support posts 180 via a plurality of tethers 150
or hinges symmetrically disposed around the movable electrode
140.
[0077] In some implementations, the tethers 150 are tangential to
the movable electrode 140 and can reduce the residual stress in the
EMS device. Other configurations for tethers 150, including
straight, curved, or folded, are also possible. The deflection of
the movable electrode 140 towards the stationary electrode 160 can
increase as the compliance of the tethers 150 increases. In
particular, the compliance of the tethers 150 can vary linearly
with the inverse of its width, and can vary directly with the cube
of its length. Thus, the tethers 150 can be longer and thinner so
as to increase the deflection of the movable electrode 140.
Moreover, the tethers 150 can be made of the same material and have
substantially the same compliance, which can lead to a
substantially uniform deflection for the movable electrode 140. For
example, each of the tethers 150 can be made of metals such as
aluminum (Al) and titanium (Ti), or other materials such as silicon
(Si), oxides, nitrides, and oxynitrides.
[0078] In some implementations, the substrate 200 can be a
transparent substrate such as glass, plastic, or other transparent
material. In some implementations, the substrate 200 can be a glass
substrate having a thickness of at least 700 .mu.m. The stationary
electrode 160 can be formed on the substrate 200. The stationary
electrode 160 can include an optical stack (not shown). The optical
stack can include an absorber layer and/or a plurality of other
layers, and can be configured similar to the optical stack 16 in
FIGS. 3A-3E. The absorber layer can have a thickness between about
20 .ANG. and about 100 .ANG., and can be made of electrically
conductive material such as MoCr.
[0079] In some implementations, the movable electrode 140 can be
substantially square or rectangular, and positioned directly over
the stationary electrode 160. In some implementations, the movable
electrode 140 can be between about 4000 .ANG. and about 60000 .ANG.
thick. In the example illustrated in FIG. 9, the EMS device with
movable electrode 140 can form part of a pixel in a display
device.
[0080] The movable electrode 140 can include a plurality of layers
(not shown), including but not limited to a reflective layer and a
deformable layer. In such a configuration, the optical properties
of the movable electrode 140 can be decoupled from its mechanical
properties. The reflective layer can include a plurality of
sub-layers (not shown). For example, the reflective layer can
include a dielectric sub-layer having a thickness between about
4000 .ANG. and about 40000 .ANG. to provide structural rigidity to
the movable electrode 140, a metal sub-layer having a thickness
between about 100 .ANG. and about 500 .ANG., and a reflective
sub-layer having a thickness between about 100 .ANG. and about 500
.ANG.. Furthermore, the deformable layer can include a plurality of
sub-layers (not shown). The deformable layer have a thickness
between about 2000 .ANG. and about 20000 .ANG. and can include one
or more dielectric sub-layers, and a conductive sub-layer having a
thickness between about 100 .ANG. and about 500 .ANG.. Each of the
dielectric sub-layers described above can include dielectric
materials such as nitrous oxide, silicon dioxide, silicon
oxynitride, and silicon nitride. Each of the metal or conductive
sub-layers described above can include aluminum, copper,
aluminum-copper alloy, or other electrically conductive material.
Each of the reflective sub-layers described above can include Al,
Al alloy, or other reflective material. In some implementations,
the reflective layer and the deformable layer of the movable
electrode 140 form part of an AIMOD.
[0081] The movable electrode 140 is configured to electrostatically
actuate towards the stationary electrode 160 when a voltage is
applied to the movable electrode 140. Each of the tethers 150 can
bend and the movable electrode 140 can deflect towards the
stationary electrode 160. If the movable electrode 140 includes a
reflective layer and a deformable layer, the deflection for
actuation can be undertaken by the deformable layer so as to reduce
distortion in the reflective layer from bending in the peripheral
regions. The movable electrode 140 remains substantially parallel
to the stationary electrode 160 during actuation. However, as
applied voltage to the movable electrode 140 increases, the EMS
device may have a limited stable range before snap-through.
[0082] The movable electrode 140 and the stationary electrode 160
define a gap therebetween, so that in some implementations, a gap
distance between the movable electrode 140 and the stationary
electrode 160 can influence the reflective properties of the EMS
device. The EMS device can move to three or more positions across
the gap upon electrostatic actuation, such as in an AIMOD. The
AIMOD can be designed to be viewed from the substrate 200 side of
the AIMOD, meaning that incident light enters the AIMOD through the
substrate 200. Depending on the position of the movable electrode
140, different wavelengths of light are reflected back through the
substrate 200, which gives the appearance of different colors.
[0083] FIG. 10A shows a perspective top view of an example of a
movable electrode of an EMS device having a plurality of
protrusions. FIG. 10B shows a perspective bottom view of an example
of the movable electrode of the EMS device in FIG. 10A. The
protrusions 100 also may be referred to as "dimples." In some
implementations as illustrated in the example in FIGS. 10A and 10B,
the protrusions 100 can be positioned on tethers 150 symmetrically
disposed around the movable electrode 140. The protrusions 100 can
connect to and extend from the surface of the tethers 150 facing
the stationary electrode 160 or the substrate 200 in FIG. 9.
[0084] As the tethers 150 can be symmetrically disposed around the
movable electrode 140, the protrusions 100 also can be
symmetrically disposed around the movable electrode 140. The
protrusions 100 can be rotationally symmetric about the center of
the movable electrode 140. Each of the protrusions 100 can be
positioned proximate to where the tethers 150 attach to the movable
electrode 140. In the example in FIGS. 10A and 10B, four
protrusions 100 on tethers 150 are disposed around the periphery of
the movable electrode 140. However, it is understood that fewer
protrusions 100 or more protrusions 100 can be disposed around the
periphery of the movable electrode 140.
[0085] The protrusions 100 may be mounted, attached, joined,
connected, formed, or otherwise positioned on the tethers 150. The
protrusions 100 may be formed as part of and as extensions from the
tethers 150 themselves. In some implementations, one or more
protrusions 100 may be positioned on the surface of the movable
electrode 140 and facing the stationary electrode 160 as discussed
in more detail in FIG. 10C. In some implementations, one or more
protrusions may be positioned on the surface of the substrate 200
or the stationary electrode 160 as discussed in more detail in FIG.
10D.
[0086] In some implementations, the protrusions 100 can be
positioned on the movable electrode 140 rather than or in addition
to the tethers 150. FIG. 10C shows a perspective bottom view of an
example of a movable electrode of an EMS device having a plurality
of protrusions on the movable electrode. Each of the four
protrusions 100 in FIG. 10 can be positioned proximate the corners
of the movable electrode 140. The movable electrode 140 can bend in
regions between the protrusions 100. In some implementations, the
protrusions 100 can be positioned around a center of the movable
electrode 140 so that the protrusions 100 can pivot about the
center of the movable electrode 140. While three or more
protrusions 100 can provide increased stability for the movable
electrode 140, it is understood that fewer protrusions can be
positioned on the movable electrode 140. For example, one
protrusion 100 can be positioned at the center of the bottom
surface of the movable electrode 140. In some implementations, the
protrusions 100 can be positioned on the movable electrode 140 and
the tethers 150.
[0087] In some implementations, the protrusions 100 can be
positioned on the stationary electrode 160 or the substrate 200.
FIG. 10D shows an example of a cross-sectional schematic view of an
EMS device with at least one protrusion on the substrate making
contact with one of the tethers. In the example in FIG. 10D, two
protrusions 100 are formed on the substrate 200. As the movable
electrode 140 actuates towards the substrate 200, at least one of
the protrusions 100 makes contact with one of the tethers 150. As
the movable electrode 140 continues to move, the one of the tethers
150 can make contact with a second protrusion 100 on the substrate
200. The tethers 150 may have a non-rigid surface so that when the
at least one protrusion 100 makes contact, the region between the
at least one protrusion 100 and the support post 180 can bend. In
some implementations, the protrusions 100 may make contact with the
movable electrode 140 instead of or in addition to the tethers
150.
[0088] As discussed earlier herein, when the movable electrode 140
is electrostatically actuated towards the stationary electrode 160
in FIG. 9 or FIG. 10D, the movable electrode 140 may snap-through
towards the stationary electrode 160 upon moving beyond the stable
range. However, with the protrusions 100 provided on the bottom
surface of the tethers 150, on the substrate 200 or the stationary
electrode 160, or on the movable electrode 140, the protrusions 100
may make contact with any surface of the EMS device during
actuation of the movable electrode 140. Any surface of the EMS
device may include but is not limited to the top surface of the
substrate 200, the top surface of the stationary electrode 160, the
bottom surface of the movable electrode 140, the bottom surface of
the tethers 150, and any of the surfaces of the support posts
180.
[0089] When any of the protrusions 100 make contact with a surface
of the EMS device, the one or more protrusions 100 can increase the
overall stiffness of the EMS device. The stiffness of the EMS
device increases in effect because the protrusions 100 shorten the
effective length of the tethers 150 or movable electrode 140. As
discussed earlier herein, the stiffness is approximately cubic with
effective length. As a result, the positioning of the protrusions
100 relative to the tethers 150 or movable electrode 140 may vary
the stiffness of the EMS device upon contact. In addition, the
relative size of the protrusions 100 also may vary the stiffness of
the EMS device upon contact. The one or more protrusions 100
provide increased resistance to deformation of the tethers 150 or
movable electrode 140. In some implementations, for example, the
protrusions 100 change the compliance of the tethers 150 or movable
electrode 140 so that the movable electrode 140 continues to move
towards the stationary electrode 160 while reducing the effects of
snap-through.
[0090] The protrusions 100 may be connected to or make contact with
a non-rigid surface of the EMS device. For example, in some
implementations, the protrusions 100 can be connected to a
non-rigid surface of the movable electrode 140 or the tethers 150.
As the protrusions 100 make contact with another surface of the EMS
device, the protrusions 100 can cause the non-rigid surface to
flex. Thus, as the movable electrode 140 continues to move, the
regions on the tethers 150 or on the movable electrode 140 where
the protrusions 100 are not in contact will effectively bend.
[0091] In some implementations, the protrusions 100 may make
contact with a non-rigid surface of the movable electrode 140 or
tethers 150. The protrusions 100 may be connected to or otherwise
positioned on the substrate 200 or the stationary electrode 160,
and need not be connected to a non-rigid surface. During actuation,
as the protrusions 100 make contact with a non-rigid surface of the
movable electrode 140 or the tethers 150 to cause the non-rigid
surface to flex. Hence, as the movable electrode 140 continues to
move, the regions on the tethers 150 or on the movable electrode
140 where the protrusions 100 are not in contact will effectively
bend.
[0092] While the protrusions 100 themselves need not be made of
compliant or flexible material, the protrusions 100 may be
connected to or make contact with a compliant or non-rigid surface
of the EMS device. Thus, the protrusions 100 may increase the
overall stiffness of the EMS device upon contact with any surface
of the EMS device without stopping the EMS device altogether.
Rather than having protrusions 100 prevent contact of the movable
electrode 140 with the stationary electrode 160, the protrusions
100 change the compliance of the movable electrode 140 and/or
tethers 150 while allowing the movable electrode 140 to continue to
move even after the protrusions 100 contact a surface of the EMS
device. Therefore, upon contact with another surface of the EMS
device, protrusions 100 may slow the effects of snap-through by
making the movable electrode 140 and/or tethers 150 more resistant
to force. Generally, the movable electrode 140 collapses towards
the stationary electrode 160 when the electrostatic force is
greater than the mechanical restoring force of the tethers 150 and
the movable electrode 140. Contact of the protrusions 100 with any
surface of the EMS device increases the mechanical restoring force
so that the electrostatic force needs to be increased to a greater
degree to overcome restoring force. Depending on the size and
number of the protrusions 100, the mechanical restoring force can
be even larger. Hence, the protrusions 100 can increase the overall
stiffness of the system and slow the effects of snap-through,
allowing for additional stable regions across the electrical
gap.
[0093] In some implementations, the thickness or height, h, of the
protrusions 100 can be greater than about 20 nm. Generally, the
protrusions 100 can have a height greater than the inherent surface
roughness or topography of the electrodes. The protrusions 100 also
can have a height greater than the dimensions of bumps typically
provided primarily for anti-stiction purposes. In some
implementations, the height of the protrusions 100 can be between
about 20 nm and about 4000 nm (limited by the initial gap
distance), such as between about 100 nm and about 200 nm.
[0094] The height of the protrusions 100 can depend on the desired
stable region of the gap between the movable electrode 140 and the
stationary electrode 160. Specifically, the desired gap distance
can be stabilized by adjusting the height of the protrusions 100
accordingly. For example, in some implementations, if the height of
the protrusions 100 is about 140 nm, then the EMS device can be
stabilized at a gap distance of about 140 nm. Thus, the presence of
protrusions 100 can create additional stable states across the gap
of the EMS device.
[0095] In some implementations, each of the protrusions 100 can
have a different height. As such, each of the protrusions 100 can
contact a surface of the EMS device successively, which can thereby
provide additional stable states of operation. For example, one of
the protrusions 100 with a first height can provide a first stable
state, and another one of the protrusions 100 with a second height
different from the first height can provide a second stable state
different from the first stable state, and so on. Thus, a taller
protrusion 100 can make contact with the EMS device first, and then
a shorter protrusion 100 can make contact with the EMS device
second, so that at least two stable states can be provided. This
can provide a "staircase response" as the applied voltage to the
movable electrode 140 increases for a more digital operation of the
EMS device.
[0096] In some implementations, the EMS device can be a
two-terminal or three-terminal device (not shown). In a
three-terminal device, the EMS device can include multiple
electrodes and multiple gaps. In some implementations, the
three-terminal device enables the movable electrode to actuate in
two different directions towards two different electrodes, thereby
increasing the stable region of operation of the EMS device. For
example, the EMS device can include a top electrode over the
movable electrode and a bottom electrode below the movable
electrode, such that the movable electrode is configured to move
across an upper gap by electrostatic actuation between the movable
electrode and the top electrode and across a lower gap by
electrostatic actuation between the movable electrode and the
bottom electrode.
[0097] FIGS. 11A-11E are cross-sectional illustrations of various
stages in a process of manufacturing an EMS device having a
plurality of protrusions.
[0098] In the example in FIG. 11A, an implementation of an EMS
device with a substrate 200 can be provided. It is understood that
the substrate 200 can include one or more layers and sub-layers,
such as optical stacks and conductive layers. Each of the layers
and sub-layers of the EMS device can be deposited using techniques
known in the art, such as physical vapor deposition (PVD), chemical
vapor deposition (CVD), plasma-enhanced chemical vapor deposition
(PECVD), atomic layer deposition (ALD), and spin-coating.
Additionally, each of the layers and sub-layers can be patterned by
masking and etching processes known in the art.
[0099] The example in FIG. 11A illustrates deposition of
sacrificial layer 250a on the substrate 200. The sacrificial layer
250a can be deposited using any of the deposition techniques
discussed earlier herein. The formation of sacrificial layer 250a
can include deposition of an etchable material such as Mo or
amorphous Si. The thickness of the sacrificial layer 250a can be
configured to the desired height of one or more protrusions.
[0100] In the example in FIG. 11B, a portion of the sacrificial
layer 250a can be etched. The etching process can be performed with
one or more patterning, masking, and/or etching processes.
Patterning and masking techniques can include photolithography, and
etching techniques can include wet etching or dry etching. The
portion of the sacrificial layer 250a that is etched defines one or
more cavities that correspond to where the one or more protrusions
are to be positioned. Thus, the sacrificial layer 250 serves as a
mold for the one or more protrusions. It is understood that even
though only two cavities are depicted in the example in FIG. 11B,
fewer or more cavities can be formed within the sacrificial layer
250a.
[0101] The example in FIG. 11C illustrates deposition of
sacrificial layer 250b on sacrificial layer 250a. In some
implementations, the material of sacrificial layer 250b can be the
same material as sacrificial layer 250a. The sacrificial layer 250b
can be deposited using any of the deposition techniques described
earlier herein. The thickness of the sacrificial layer 250b can be
configured so that the combined thicknesses of the sacrificial
layers 250a and 250b establishes a desired initial gap distance
from the movable electrode 140 to the substrate 200.
[0102] The example in FIG. 11D illustrates deposition of a movable
electrode 140 over the sacrificial layer 250b. The movable
electrode 140 can be deposited using any of the deposition
techniques described earlier herein. The movable electrode 140 can
be made of one or more layers and sub-layers, including but not
limited to a reflective (e.g., mirror) layer and a deformable
layer. In some implementations as illustrated in the example in
FIG. 11D, the movable electrode 140 can include protrusions 100
extending from a surface of the movable electrode 140 facing the
substrate 200. Hence, the protrusions 100 can be made of the same
material as the movable electrode 140. In some implementations, for
example, the protrusions 100 and the movable electrode 140 can be
made of Al or Al alloy. The compliance of the movable electrode 140
may vary according to the designed width, length, and position of
the protrusions 100.
[0103] The example in FIG. 11E illustrates removal of sacrificial
layers 250a and 250b to release the movable electrode 140. A cavity
190 is formed upon exposing sacrificial layers 250a and 250b to an
etchant. The cavity 190 has a desired initial gap distance between
the movable electrode 140 and the substrate 200. After removal of
the sacrificial layers 250a and 250b, the movable electrode 140 is
movable across the cavity 190. As the movable electrode 140 travels
across the cavity 190 towards the substrate 200, the protrusions
100 contact the substrate 200 so that the height of the protrusions
100 positions the movable electrode 140 at a stable state.
[0104] FIG. 12 is an example of a graph illustrating a hysteresis
curve for a position of a movable electrode as a function of
applied voltage of an EMS device. In some implementations, the EMS
device is part of an optical device. The EMS device can have one or
more protrusions as described earlier herein. The protrusions may
be configured to provide a stable color range corresponding at
least in part to the heights of the protrusions. FIG. 12 is an
example of the gap distance between a movable electrode and a
stationary electrode of an IMOD as a function of applied voltage
(V). Each of the data points provided in the hysteresis curve can
correspond to a different color state.
[0105] The IMOD has a hysteresis property providing ranges in which
the IMOD is stable. Between about 0 V and 6 V, the gap is
relatively stable between about 540 nm and about 360 nm. This
relatively stable range can provide access to a broad color gamut
for the IMOD, including the red-green-blue color spectrum. However,
when about 6 V is applied, the gap distance decreases substantially
until about 140 nm. Between about 6 V and 13 V, the IMOD remains
relatively stable in this range, which provides a stable black
state. In other words, the movable electrode is not as sensitive to
changes in voltage within this range. In this range, one or more
protrusions provided on the movable electrode or tethers of the
IMOD are in contact with a surface of the IMOD, such as the top
surface of the substrate or the stationary electrode. In some
implementations, the one or more protrusions may be provided on the
substrate or stationary electrode to contact a surface of the
movable electrode or tethers. Beyond 13 V, the gap distance
decreases substantially until the IMOD reaches another stable
state, which can be a white state. At this state, the movable
electrode and the stationary electrode can be substantially closed
so that the gap distance is almost or about 0 nm.
[0106] When the voltage is reduced from that value, the movable
electrode remains in this stable state (such as the white state)
until the voltage drops back below about 10 V. As the voltage is
reduced from about 10V, between about 9 V and about 2 V, the
movable electrode is stabilized in another stable state, which can
be the black state. When the applied voltage is reduced to less
than about 2 V, the gap distance increases substantially until the
movable electrode reaches near the initial gap distance, which can
be about 540 nm.
[0107] FIG. 13 is a flow diagram illustrating a method of
manufacturing an EMS device. It will be understood that additional
processes may be present. For example, deposition of additional
underlying or overlying layers can be achieved by various film
deposition processes, such as PVD, PECVD, thermal CVD, ALD, spin-on
coating, and electroplating. Patterning techniques, such as
photolithography, can be used to transfer patterns on a mask to a
layer of material. Etching processes can be performed after
patterning to remove unwanted materials. Planarization processes
such as "etch back" and chemical mechanical polishing (CMP) can be
employed to create a substantially flat surface for further
processing.
[0108] The process 1300 begins at block 1310 where a substrate is
provided. As discussed earlier herein the substrate can be formed
of a substantially transparent material, such as glass or plastic.
In some implementations, the substrate 200 can be a glass substrate
having a thickness of at least 700 .mu.m.
[0109] The process 1300 continues at block 1320 where a stationary
electrode is formed over the substrate. In some implementations,
the stationary electrode can include an optical stack. The optical
stack can include an absorber and/or a plurality of other layers
and/or sub-layers. The absorber can include electrically conductive
material.
[0110] The process 1300 continues at block 1330 where a movable
electrode is formed over the stationary electrode. The movable
electrode is configured to move to three or more positions across a
gap by electrostatic actuation between the movable electrode and
the stationary electrode. In some implementations, a plurality of
tethers can be formed that are symmetrically disposed around the
edges of the movable electrode.
[0111] The process continues at block 1340 where a protrusion is
formed on a surface of the EMS device. The protrusion is configured
to change the stiffness of the EMS device when in contact with
another surface of the EMS device at one of the positions across
the gap. At least one of the surfaces in contact with the
protrusion is non-rigid. In some implementations, the protrusion
can be connected to at least one of the tethers. In some
implementations, the protrusion can be part of a plurality of
protrusions, where each of the protrusions is connected to each of
the tethers. In some implementations, the protrusion can be
connected to a surface of the movable electrode. In some
implementations, the protrusion can be connected to or otherwise
positioned on the substrate or stationary electrode. In some
implementations, the protrusion can have a height greater than
about 20 nm. Typically, the protrusion can have a height greater
than the inherent surface roughness of the electrodes and greater
than the dimensions of bumps provided primarily for anti-stiction
purposes.
[0112] FIGS. 14A and 14B are system block diagrams illustrating a
display device 40 that includes a plurality of IMOD display
elements. The display device 40 can be, for example, a smart phone,
a cellular or mobile telephone. However, the same components of the
display device 40 or slight variations thereof are also
illustrative of various types of display devices such as
televisions, computers, tablets, e-readers, hand-held devices and
portable media devices.
[0113] The display device 40 includes a housing 41, a display 30,
an antenna 43, a speaker 45, an input device 48 and a microphone
46. The housing 41 can be formed from any of a variety of
manufacturing processes, including injection molding, and vacuum
forming. In addition, the housing 41 may be made from any of a
variety of materials, including, but not limited to: plastic,
metal, glass, rubber and ceramic, or a combination thereof. The
housing 41 can include removable portions (not shown) that may be
interchanged with other removable portions of different color, or
containing different logos, pictures, or symbols.
[0114] The display 30 may be any of a variety of displays,
including a bi-stable or analog display, as described herein. The
display 30 also can be configured to include a flat-panel display,
such as plasma, EL, OLED, STN LCD, or TFT LCD, or a non-flat-panel
display, such as a CRT or other tube device. In addition, the
display 30 can include an IMOD-based display, as described
herein.
[0115] The components of the display device 40 are schematically
illustrated in FIG. 14A. The display device 40 includes a housing
41 and can include additional components at least partially
enclosed therein. For example, the display device 40 includes a
network interface 27 that includes an antenna 43 which can be
coupled to a transceiver 47. The network interface 27 may be a
source for image data that could be displayed on the display device
40. Accordingly, the network interface 27 is one example of an
image source module, but the processor 21 and the input device 48
also may serve as an image source module. The transceiver 47 is
connected to a processor 21, which is connected to conditioning
hardware 52. The conditioning hardware 52 may be configured to
condition a signal (such as filter or otherwise manipulate a
signal). The conditioning hardware 52 can be connected to a speaker
45 and a microphone 46. The processor 21 also can be connected to
an input device 48 and a driver controller 29. The driver
controller 29 can be coupled to a frame buffer 28, and to an array
driver 22, which in turn can be coupled to a display array 30. One
or more elements in the display device 40, including elements not
specifically depicted in FIG. 14A, can be configured to function as
a memory device and be configured to communicate with the processor
21. In some implementations, a power supply 50 can provide power to
substantially all components in the particular display device 40
design.
[0116] The network interface 27 includes the antenna 43 and the
transceiver 47 so that the display device 40 can communicate with
one or more devices over a network. The network interface 27 also
may have some processing capabilities to relieve, for example, data
processing requirements of the processor 21. The antenna 43 can
transmit and receive signals. In some implementations, the antenna
43 transmits and receives RF signals according to the IEEE 16.11
standard, including IEEE 16.11(a), (b), or (g), or the IEEE 802.11
standard, including IEEE 802.11a, b, g, n, and further
implementations thereof. In some other implementations, the antenna
43 transmits and receives RF signals according to the
Bluetooth.RTM. standard. In the case of a cellular telephone, the
antenna 43 can be designed to receive code division multiple access
(CDMA), frequency division multiple access (FDMA), time division
multiple access (TDMA), Global System for Mobile communications
(GSM), GSM/General Packet Radio Service (GPRS), Enhanced Data GSM
Environment (EDGE), Terrestrial Trunked Radio (TETRA),
Wideband-CDMA (W-CDMA), Evolution Data Optimized (EV-DO), 1xEV-DO,
EV-DO Rev A, EV-DO Rev B, High Speed Packet Access (HSPA), High
Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet
Access (HSUPA), Evolved High Speed Packet Access (HSPA+), Long Term
Evolution (LTE), AMPS, or other known signals that are used to
communicate within a wireless network, such as a system utilizing
3G, 4G or 5G technology. The transceiver 47 can pre-process the
signals received from the antenna 43 so that they may be received
by and further manipulated by the processor 21. The transceiver 47
also can process signals received from the processor 21 so that
they may be transmitted from the display device 40 via the antenna
43.
[0117] In some implementations, the transceiver 47 can be replaced
by a receiver. In addition, in some implementations, the network
interface 27 can be replaced by an image source, which can store or
generate image data to be sent to the processor 21. The processor
21 can control the overall operation of the display device 40. The
processor 21 receives data, such as compressed image data from the
network interface 27 or an image source, and processes the data
into raw image data or into a format that can be readily processed
into raw image data. The processor 21 can send the processed data
to the driver controller 29 or to the frame buffer 28 for storage.
Raw data typically refers to the information that identifies the
image characteristics at each location within an image. For
example, such image characteristics can include color, saturation
and gray-scale level.
[0118] The processor 21 can include a microcontroller, CPU, or
logic unit to control operation of the display device 40. The
conditioning hardware 52 may include amplifiers and filters for
transmitting signals to the speaker 45, and for receiving signals
from the microphone 46. The conditioning hardware 52 may be
discrete components within the display device 40, or may be
incorporated within the processor 21 or other components.
[0119] The driver controller 29 can take the raw image data
generated by the processor 21 either directly from the processor 21
or from the frame buffer 28 and can re-format the raw image data
appropriately for high speed transmission to the array driver 22.
In some implementations, the driver controller 29 can re-format the
raw image data into a data flow having a raster-like format, such
that it has a time order suitable for scanning across the display
array 30. Then the driver controller 29 sends the formatted
information to the array driver 22. Although a driver controller
29, such as an LCD controller, is often associated with the system
processor 21 as a stand-alone Integrated Circuit (IC), such
controllers may be implemented in many ways. For example,
controllers may be embedded in the processor 21 as hardware,
embedded in the processor 21 as software, or fully integrated in
hardware with the array driver 22.
[0120] The array driver 22 can receive the formatted information
from the driver controller 29 and can re-format the video data into
a parallel set of waveforms that are applied many times per second
to the hundreds, and sometimes thousands (or more), of leads coming
from the display's x-y matrix of display elements.
[0121] In some implementations, the driver controller 29, the array
driver 22, and the display array 30 are appropriate for any of the
types of displays described herein. For example, the driver
controller 29 can be a conventional display controller or a
bi-stable display controller (such as an IMOD display element
controller). Additionally, the array driver 22 can be a
conventional driver or a bi-stable display driver (such as an IMOD
display element driver). Moreover, the display array 30 can be a
conventional display array or a bi-stable display array (such as a
display including an array of IMOD display elements). In some
implementations, the driver controller 29 can be integrated with
the array driver 22. Such an implementation can be useful in highly
integrated systems, for example, mobile phones, portable-electronic
devices, watches or small-area displays.
[0122] In some implementations, the input device 48 can be
configured to allow, for example, a user to control the operation
of the display device 40. The input device 48 can include a keypad,
such as a QWERTY keyboard or a telephone keypad, a button, a
switch, a rocker, a touch-sensitive screen, a touch-sensitive
screen integrated with the display array 30, or a pressure- or
heat-sensitive membrane. The microphone 46 can be configured as an
input device for the display device 40. In some implementations,
voice commands through the microphone 46 can be used for
controlling operations of the display device 40.
[0123] The power supply 50 can include a variety of energy storage
devices. For example, the power supply 50 can be a rechargeable
battery, such as a nickel-cadmium battery or a lithium-ion battery.
In implementations using a rechargeable battery, the rechargeable
battery may be chargeable using power coming from, for example, a
wall socket or a photovoltaic device or array. Alternatively, the
rechargeable battery can be wirelessly chargeable. The power supply
50 also can be a renewable energy source, a capacitor, or a solar
cell, including a plastic solar cell or solar-cell paint. The power
supply 50 also can be configured to receive power from a wall
outlet.
[0124] In some implementations, control programmability resides in
the driver controller 29 which can be located in several places in
the electronic display system. In some other implementations,
control programmability resides in the array driver 22. The
above-described optimization may be implemented in any number of
hardware and/or software components and in various
configurations.
[0125] As used herein, a phrase referring to "at least one of" a
list of items refers to any combination of those items, including
single members. As an example, "at least one of: a, b, or c" is
intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
[0126] The various illustrative logics, logical blocks, modules,
circuits and algorithm steps described in connection with the
implementations disclosed herein may be implemented as electronic
hardware, computer software, or combinations of both. The
interchangeability of hardware and software has been described
generally, in terms of functionality, and illustrated in the
various illustrative components, blocks, modules, circuits and
steps described above. Whether such functionality is implemented in
hardware or software depends upon the particular application and
design constraints imposed on the overall system.
[0127] The hardware and data processing apparatus used to implement
the various illustrative logics, logical blocks, modules and
circuits described in connection with the aspects disclosed herein
may be implemented or performed with a general purpose single- or
multi-chip processor, a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a field
programmable gate array (FPGA) or other programmable logic device,
discrete gate or transistor logic, discrete hardware components, or
any combination thereof designed to perform the functions described
herein. A general purpose processor may be a microprocessor, or,
any conventional processor, controller, microcontroller, or state
machine. A processor also may be implemented as a combination of
computing devices, such as a combination of a DSP and a
microprocessor, a plurality of microprocessors, one or more
microprocessors in conjunction with a DSP core, or any other such
configuration. In some implementations, particular steps and
methods may be performed by circuitry that is specific to a given
function.
[0128] In one or more aspects, the functions described may be
implemented in hardware, digital electronic circuitry, computer
software, firmware, including the structures disclosed in this
specification and their structural equivalents thereof, or in any
combination thereof. Implementations of the subject matter
described in this specification also can be implemented as one or
more computer programs, i.e., one or more modules of computer
program instructions, encoded on a computer storage media for
execution by, or to control the operation of, data processing
apparatus.
[0129] Various modifications to the implementations described in
this disclosure may be readily apparent to those skilled in the
art, and the generic principles defined herein may be applied to
other implementations without departing from the spirit or scope of
this disclosure. Thus, the claims are not intended to be limited to
the implementations shown herein, but are to be accorded the widest
scope consistent with this disclosure, the principles and the novel
features disclosed herein. Additionally, a person having ordinary
skill in the art will readily appreciate, the terms "upper" and
"lower" are sometimes used for ease of describing the figures, and
indicate relative positions corresponding to the orientation of the
figure on a properly oriented page, and may not reflect the proper
orientation of, e.g., an IMOD display element as implemented.
[0130] Certain features that are described in this specification in
the context of separate implementations also can be implemented in
combination in a single implementation. Conversely, various
features that are described in the context of a single
implementation also can be implemented in multiple implementations
separately or in any suitable subcombination. Moreover, although
features may be described above as acting in certain combinations
and even initially claimed as such, one or more features from a
claimed combination can in some cases be excised from the
combination, and the claimed combination may be directed to a
subcombination or variation of a subcombination.
[0131] Similarly, while operations are depicted in the drawings in
a particular order, a person having ordinary skill in the art will
readily recognize that such operations need not be performed in the
particular order shown or in sequential order, or that all
illustrated operations be performed, to achieve desirable results.
Further, the drawings may schematically depict one more example
processes in the form of a flow diagram. However, other operations
that are not depicted can be incorporated in the example processes
that are schematically illustrated. For example, one or more
additional operations can be performed before, after,
simultaneously, or between any of the illustrated operations. In
certain circumstances, multitasking and parallel processing may be
advantageous. Moreover, the separation of various system components
in the implementations described above should not be understood as
requiring such separation in all implementations, and it should be
understood that the described program components and systems can
generally be integrated together in a single software product or
packaged into multiple software products. Additionally, other
implementations are within the scope of the following claims. In
some cases, the actions recited in the claims can be performed in a
different order and still achieve desirable results.
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